mitchell



J. R. MITCHELL.

Portable Steam Boiler.

Patented Aug. 24,1880.

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JOSEPH R. MITCHELL, OF SAN FRANCISCO, CALIFORNIA.

PORTABLE STEAM-BOILER.

SPECIFICATION forming part of Letters Patent No. 231,443, dated August 24, 1880.

Application filed November 15, 1879.

To all whom it may concern:

Be it known that I, J OSEPH RAMSDEN bIITCII- ELL, of San Francisco, in the county of San Francisco and State of California, have invented a certain new and useful invention or Improvement in Portable Steam-Boilers, which invention is fully described in the following specification and accompanying drawings.

My invention has for its object to provide an improved portable steam-boiler for thrashingengines and other purposes, which is mainly adapted to the burning of straw and other light material as fuel, and whereby a much better steam-producing surface is provided and a stronger boiler.

It consists in the combination and arrangement of an ordinary undenfired tubularboiler with water-legs attached to each side and extending down a few inches below the gratebars, water-communication being made with the boiler.

It also consists of a coil of pipe which extends across the fire-box, connecting the two water-legs, and a-iso serving the purpose of a grate; also, of a coil of pipe at the rear end of the boiler, which connects with the two waterlegs and the tube-sheet just below the waterline; also, of a drum at the rear end of the bottom of the boiler, from which extends a pipe having branches which lead into the water legs, and of other details of construction to be herein after more fully described.

In the drawings, Figure 1 is a front-end view of my improved boiler. Fig. 2 is a rear-end view of the same with a portion broken away. Fig. 3 is a longitudinal vertical section. Fig. 4 is a vertical cross-section on the line X X of Fig. 3. Fig. 5 is a detail View, showing the manner in which the water-leg is secured to the tubular boiler. Fig. 6 is a detail view, showing a modification of the fire-door.

A represents an ordinary tubular boiler arranged for under-firing, having suitable spaces at either end for combustion-chamber and to pass off the products of combustion, which pass through the small tubes wand up the chimney b. At each side of the boiler, about midway thereon, I connect water-legs B B by bolts and rivets in the usual way. These water-legs extend down on each side to a few inches below the grate-barsor to the ash-pit.

The said water-legs form the sides of the firebox or furnace, which extends from one end of the boiler to the other. Theyqnake watercominunication with the boiler by means of holes or openings 0 c 0, made between the two lines of rivets by which the boiler and waterlegs are connected, also by pipe-connections as hereinafter described.

The inside sheet of the water-leg is formed to fit the shell of the boiler for a suitable distance, as shown in Fig. 5, to bring its upper edge on a line with the upper edge of the outside sheet. It is then riveted to the boiler by the lower line of rivets. The outside sheetis riveted also, as shown in Fig. 5. The rivets pass through the shell of the boiler, the extended end of the inside sheet, and the outside sheet. By this means I have two thicknesses of boileriron where the boiler is weakened by holes being cut for water-communication between the water-legs and boiler. I thus keep the boilershell of uniform strength.

By making the boiler as described, with water-legs attached, I obtain the full tensile strength of the iron, as the pressure is all internal and no stay-bars or braces are needed. Only stay-bolts for the water-legs will be required. I also utilize the space occupied by the large flue in the return-flue straw-burner boilers by using tubes, thus obtaining equal heating-surface with a much smaller diameter of shell, and making a strong compact boiler capable of bearing high-pressure steam with perfect safety, which is of great importance in a point of economy, enabling me to reduce the size and weight of boiler and engine, as well as the amount of water and fuel required to do a given amount of work.

Between the two sections of boiler-iron forming the fire front of furnace a curved brace, O, is secured in any suitable manner, and attached to the front end of the water-legs and boiler by rivets or bolts, thus serving as alateral brace to the water-legs, as well as a support to the boiler proper.

In the front end of furnace or fire-box I construct a coil of water-pipe, D, the ends of which enter the water-legs. This pipe serves as a water-connection between the two waterlegs, also as grate-bars.

Near the rear or back end of the boiler I rivet to its lower surface a drum, E, which passes through the bottom of the back end of the furnace and is attached in any suitable manner to it. By means of this drum-connection with the furnace-bottom to which it is securely attached I obtain a rigid lateral support for the water-legs. \Vhen a very short compact boiler is required the water-legs may extend around each end of the boiler, tlms giving lateral stiffness and strength.

To the bottom ot'the drum I I attach a waterpipe, F, which extends forward, where branches are formed which connect with the water-legs on each side, as shown.

An inside connection of pipes and waterlegs may be made when outside room needs to be ecouomized. These pipes serve as watercommunicati'n between boiler and water-legs.

From about the center of the boiler toward the rear end I cut the water-legs angling to give room for the vertical play of the axle. At that end I place a curved bolster, (I, which is secured to the water-legs, and a king-bolt passesthrough it, to which the axle is attached.

At the rear end of the boiler in the combustion-chamber I place a coil of pipe, I, with its upper end entering the tube-sheet just below the waterline, the lower portions of the coil forming branches I I, which enterthe waterlegs. This coil serves as a watercommunication between the water-legs and boiler.

My furnace-door I construct double-that is tosay,a small door made in a largedoor. The large door 1s used for putting in large or crooked sticks of wood, the small door for common use. Fig. 6 shows a removable nozzle or mouth-piece, or, attached in any suitable manner in the small doorway. It is used asa guide when feeding straw into the furnace as a fuel.

To the front end of boiler A and water-legs I II, I attach in a suitable manner a shield or apron, Y, as a wind-guard, to prevent fragments of burning straw being blown from the furnace-door into the stubble.

Having thus described my invention, what I claim, and desire to secure by Letters Pat cut, is-

1. The combination of the boiler A, drum E, with its branches F, communicating Waterlegs I3 B, and pipes I) I, the latter having branches 1 I, all arranged as and for the purpose specified.

2. In combination with the boiler A and water-legs ll 13, the drum E, connected to the bottom wall of the main flue, and stay-bracing U, constructed and arranged as shown and described, for the purpose of resisting lateral strain, as specified.

8. In a portable steam-boiler,the water-legs I) B, with angles, as shown, to afford space for the vertical play of the axle, in combination with the curved bolster G, substantially as specified.

In testimony thatI claim the foregoing I have hereunto set my hand and seal thisltith day of October, 1879.

JOSE III It. MITCH E LL. 

